1. Field of the Invention
The present invention relates to a surface mount type piezoelectric vibrator molding a periphery of a piezoelectric vibrator with a resin and a method for manufacturing the same, an oscillator, electronic unit and wave clock having the surface mount type piezoelectric vibrator.
2. Description of the Related Art
Piezoelectric vibrators are indispensable to the production of industrial products such as clocks, oscillators and electronic units, and used as timekeeping sources, timing sources or reference sources for signals. A cylinder-type package is commonly used as a piezoelectric vibrator package.
However, since the cylinder-type package piezoelectric vibrator is cylindrical, the position thereof unstable or two elongate lead terminals are bendable, so that. unlike other electronic parts, the cylinder-type package piezoelectric vibrator cannot be, as it is, surface-mounted using an automatic mounting machine. The cylinder-type package piezoelectric vibrator is covered with resin to allow surface mounting using an automatic mounting machine. This resin-covered type of cylinder-type package piezoelectric vibrator is known as a surface mount type piezoelectric vibrator.
FIG. 36 is a perspective view showing an appearance of a surface mount type piezoelectric vibrator and FIG. 37 is a schematic cross-sectional view showing the inside construction of a surface mount type piezoelectric vibrator with the resin cut off.
As shown in FIGS. 36 and 37, a surface mount type piezoelectric vibrator 31 has a cylinder-type package piezoelectric vibrator 6 provided in the middle. An electrode terminal 33 is provided at the tip side of an outer lead 3 for mounting onto an external substrate. The electrode terminal 33 is formed to extend from a lead frame 60. The electrode terminal 33 is shaped like a crank. One end of the electrode terminal 33 is to be bonded to the outer lead 3 while the other end is to be mounted on a substrate. The electrode terminal 33 is disposed so that the portion that is to be mounted on a substrate is directed outward of the surface mount type piezoelectric vibrator 31.
In the surface mount type piezoelectric vibrator 31, since an electrode terminal 33 is crank-shaped and is provided at the tip side of an outer lead 3 to form a lower electrode terminal 33a, the total length of the surface mount type piezoelectric vibrator 31 is long. That is, the surface mount type piezoelectric vibrator 31 is further longer than the size up to a tip of the outer lead 3 and needs the length up to a tip of the lower electrode terminal 33a, so that the surface mount type piezoelectric vibrator had the problem that the miniaturization of the surface mount type piezoelectric vibrator 31 itself had been inhibited. Recently, the miniaturization of a substrate and the reduction of the mounting area of the surface mount type piezoelectric vibrator have been strongly required due to the progress of the miniaturization of the products using the electronic units.
In order to solve the miniaturization-related problem, the electrode terminal is folded into a u-shape (for example, see FIG. 8 in JP-A-2003-32067) and the direction of the crank-shaped electrode terminal is reverse to that of the surface mount type piezoelectric vibrator 31 shown in FIG. 37 (for example, see FIG. 1 of JP-A-2003-23335).
However, in the u-shaped electrode terminal shown in JP-A-2003-32067, there are the problems as follows:
1. When a part of the lead frame is folded in cross-sectional u-shaped by a press work, each of an upper surface and a back surface are pressed hard with a die and a punch. First, those of the lead frame are folded in L-shape at the first press and next, in u-shape at the second press. However, in the press work that moves the die and punch vertically, a tip of the electrode section and the punch are interfered with each other when secondly folding in cross-sectional u-shape. Accordingly, complicated press equipments are required and it becomes difficult to work the cross-sectional u-shaped electrode terminal by the folding.
2. When using the method of welding by applying voltage for bridging the outer lead in contact with the upper electrode terminal for the electrical continuity, the outer lead and upper electrode terminals need to be in contact with each other between two upper and lower bonding electrodes, while it becomes very difficult that they are disposed between the bonding electrodes in case of the cross-sectional u-shaped electrode terminal. The reason is that the lower electrode terminal is disposed at the reverse side opposite to the outer lead of the upper electrode terminal, whereby it is increasingly difficult that the bonding electrode at the lower side directly supports the lower surface.
3. Since a vertical section between the upper electrode terminal and lower electrode terminal is arranged at the end as the surface mount type piezoelectric vibrator, it is highly possible that a solid resin burr is formed after molding resin. The reason is that in the resin mold forming, attaching a draft angle to the resin mold die is required for good de-molding between an outward form of molded product and a resin mold die and the formation of a gap therebetween is required to evade the contact with the resin mold die and the lead frame. By the necessity of the draft angle and gap, it is highly possible that a solid resin burr is formed on the vertical section. It is difficult to remove the resin burr on the vertical section by means of the general deburring.
Further, as disclosed in JP-A-2003-23335, in case when the direction of the crank-shaped electrode terminal is reverse to the direction of the surface mount type piezoelectric vibrator 31 shown in FIG. 37, there are the problem as follows.
In case of this example, since the lower electrode terminal is overlapped with the piezoelectric vibrator, the expansion section of the sealing tube may be contacted with the lower electrode terminal. If so, the function of the vibrator is hindered due to the short-circuiting of the vibrator. Consequently, so the margin may be given in the height direction as to evade the contact between the sealing tube and the lower electrode terminal, and on the other hand, there is the problem that the height of the body of the surface mount type piezoelectric vibrator increases.
Next, the method for manufacturing the conventional surface mount type piezoelectric vibrator has the following problems.
The process for manufacturing the surface mount type piezoelectric vibrator 31 includes the process for bonding the outer lead 3 of the piezoelectric vibrator 6 to the electrode terminal 33 formed from the lead frame 20, the resin mold process for coating the piezoelectric vibrator 6, the cutting process for pulling out and dropping, from the lead frame 20, a section that joins the resin mold section as the piezoelectric vibrator 6 to the lead frame 20, and the process for electrically testing the surface mount type piezoelectric vibrator 31. First of all, the problems for the respective processes will be described as follows.
[Process for Bonding an Outer Lead to an Electrode Terminal]
In the process for bonding the outer lead 3 of the surface mount type piezoelectric vibrator 31 to the upper electrode terminal 33 by bringing the outer lead 3 into contact with the upper electrode terminal of the electrode terminal 33 for electrical continuity and applying voltage, the piezoelectric vibrator 6 is transferred to each space section inside the lead frame by a predetermined transfer jig capable of conserving the piezoelectric vibrator 6, whereby the bonding is implemented.
FIGS. 38 to 40 show the conventional lead frame. FIG. 38 is a schematic perspective view, FIG. 39 is a fragmentary enlarged view of FIG. 38 and FIG. 40 is a plan view showing the arrangement of the piezoelectric vibrator on the lead frame.
As shown in FIGS. 38 and 39, a lead frame 60 for a conventional surface mount type piezoelectric vibrator has side frames 61 of a carrying and positioning section, section bars 62 and arrangement areas 64 for vibrators 6. These individual components are provided across the width of the lead frame 60 in two rows. Arrangement areas 64 for vibrators 6 are partitioned by a frame 63 for supporting electrode terminals 33 into two rows. Typically, these side frames and sections bars are generically called frame bars.
In the arrangement area 64 for the vibrator 6, a pair of electrode terminals 33 protrude from the side frame 61. A dummy terminal 32 also protrudes from a frame 63 for support the lead frame so that the dummy terminal 32 faces the electrode terminal 33. These terminals, the electrode terminal 33 and the dummy terminal 32, are disposed to face each other across the width of the lead frame 60. As shown in FIG. 35, a plurality of positioning through holes 65 are provided at predetermined intervals in each of the carrying and positioning side frames 61 of the lead frame 60.
The outer lead 3 of the vibrator 6 and the electrode terminal 33 are aligned with the above conventional lead frame 60 for welding purposes in a manner described below. A positioning reference block (not shown) is first prepared. The positioning reference block has a plurality of positioning pins for positioning the lead frame 60 provided to stand up at constant intervals in association with welding positions. The positioning reference block is aligned with the lead frame 60 by inserting the plurality of positioning pins into the plurality of corresponding positioning through holes 65 of the lead frame 60. This causes the outer lead 3 of the vibrator 6 to be aligned with the electrode terminal 33 for welding purposes.
FIG. 41 and FIG. 42 show the process for bonding the conventional piezoelectric vibrator. FIG. 41 is a schematic cross-sectional view and FIG. 42 is a schematic front view from a view of the outer lead side to explain FIG. 41.
As shown in FIG. 41, to weld outer leads 3 of the vibrator 6 to electrode terminals 33, vibrators 6 are then disposed in areas 64 in the lead frame 60 provided for arranging plurality of vibrators 6. The outer lead 3 is then placed on the upper. electrode terminal 33c of the lead frame 60, Welding is performed by placing both the outer lead 3 and the upper electrode terminal 33c between an upper bonding electrode 37 and an lower bonding electrode 36 and applying voltage to the bonding electrodes 36, 37.
In the surface mount type piezoelectric vibrator 31, there is, in particular, the problem that the piezoelectric vibrator 6 is properly aligned with the lead frame 60 by the method for bonding the upper electrode terminal 33c to the above-mentioned outer lead 3. It is necessary to satisfy 3 alignments such as the difference θ in the turning angle of the outer lead 3, a section bonding for the electrical continuity with the outer lead 3 and the position of cutting terminal of the outer lead 3 so as to align the piezoelectric vibrator 6 with the lead frame 60.
In other words, as shown in FIGS. 41 and 42, the alignment of these three points include a turning angle difference θ between a pair of two upper electrode terminals 33c and the outer lead 3, the alignment of a bonding point 33d located in the middle of the upper electrode terminal 33c with a required bonding point in the bent outer lead 3, and the handling of the length of the terminal of the outer lead 3 between the upper electrode terminal 33 and the contour of the piezoelectric vibrator. The alignment of these three points will be described below in detail.
1. The length of the part of the outer lead 3 that protrudes from the airtight terminal 1 is smaller than the contour of the sealing tube 5 of the vibrator 6. Even about a few scores of grams of load also result in the plastic deformation of the outer lead 3. Therefore, it is difficult to regulate the turning angle difference θ for the outer lead 3 with an external force. Although, therefore, the turning angle difference θ for the outer lead 3 is regulated with the dead weight of the vibrator 6, the turning angle difference θ is actually too small for alignment and a required positional accuracy is not met in some cases.
2. The bonding point 33d located in the middle of the electrode terminal 33 is coincided with a required bonding point in the bent outer lead 3. In a process for bending the outer lead 3 in advance, misalignment of the turning angle difference θ for the outer lead 3 results in an insufficient bend in the outer lead 3, thus making impossible the alignment of the required bonding point in some cases.
3. As described earlier, even a small load results in the plastic deformation of the outer lead 3. It is therefore difficult to directly regulate the length and position of the terminal of the outer lead 3 with a jig and the like. Thus, conventional positioning means having a radiused (curved) surface corresponding to the cylindrical side of the vibrator 6 is provided for alignment using the shapes of the sealing tube 5 and the airtight terminal 1 in the longitudinal direction of the vibrator 6. In a process for sealing the sealing tube 5 and the airtight terminal 1, however, there is a dimensional deviation in the longitudinal direction of the vibrator 6 with a resultant deviation in the cutting accuracy for the outer lead 3, thus making the above alignment insufficient in some cases.
Particularly machining using a transfer jig will make it impossible to proceed with subsequent processes properly under any of the above-mentioned situations.
In addition, an insufficient alignment of the sealing tube 5 described above can result in warpage in the lead frame 60 in the longitudinal direction thereof because of the contact of the dummy terminal 32 facing the electrode terminal 33 with the sealing tube 5 on the lead frame 60. Any warpage in the lead frame 60 makes it possible to proceed with subsequent processes properly when the lead frame 60 is mechanically carried and aligned.
In the resin molding process that follows the bonding process described above, an incorrect alignment of the vibrator 6 in molds also results in not only problematic electrode terminal 33 bonding. The incorrect alignment also results the problematic partial exposure of the vibrator 6 from mold resin the resultant incorrect formation of the periphery of the vibrator 6.
[Resin Mold Process]
A conventional resin mold process for a surface mount type piezoelectric vibrator 31 will be described below. A surface mount type piezoelectric vibrator 31 has a sealing tube in the middle thereof. An electrode terminal for mounting on an external substrate is provided on the tip side of an outer lead. The electrode terminal is formed to extend from a lead frame. The electrode terminal is formed like a crank. One end of the electrode terminal is to be bonded to the outer lead 3 while the other end is to be mounted on a substrate. The surface mount type piezoelectric vibrator 31 has the portion to be mounted on a substrate disposed to face outward.
In the resin mold process for the surface mount type piezoelectric vibrator 31, a vibrator 6 is coated with resin mold material at a resin-molded section formed inside a lead frame 60 space. The resin-molded section is formed of molds. The vibrator 6 is held between an upper mold and a lower mold for resin molding.
In a surface mount type package, burrs called place thickness burrs of a lead frame 60 are produced on the sides of the package and prevent an increase in outside dimensions of the package. In the surface mount type package, as shown in FIGS. 38 to 40, it is known that molds for resin mold are placed in blocks each shaped by a side frame 61 and a section bar 62 formed to surround the outside perimeter of the package and a frame 63 for supporting lead terminals for molding to form the shape of the external sides of each package.
Mold resin material is poured into the molds with a piezoelectric vibrator held between a contact portion formed on the top surface of the lower mold and the inside of the upper mold for molding purposes. This forms surface mount type piezoelectric vibrators 31 each having a resin mold portion as shown in FIG. 36 in arrangement areas 64 of the lead frame 60 for a plurality of vibrators.
However, the resin molding process for a conventional surface mount type piezoelectric vibrator 31 has problematic points as described below.
1. The size and arrangement of a mold 66 for molding the periphery of each of vibrators 6 out of resin in the lead frame 60 are as shown in FIG. 43. The mold 66 is long in the longitudinal direction of the lead frame 60.
Each of the vibrators 6 in the lead frame 60 has the longitudinal side thereof disposed across the width of the lead frame 60 as shown in FIG. 40.
The material of the lead frame 60 is conductive material such as an iron-containing alloy. An iron-containing alloy is also used for molds for resin molding. The lead frame 60 and these molds are made of the same iron-containing materials. However, each of these materials has a different coefficient of linear expansion. In resin molding, the mold 66 for resin molding and the lead frame 60 are heated to temperatures between 150 and 180° C.
The difference in coefficient of linear expansion between the mold 66 for resin molding and the lead frame 60 causes a misalignment between the mold 66 for resin molding and the lead frame 60. The misalignment appears in the longitudinal direction of the lead frame 60 can easily appear across the width of the surface mount type piezoelectric vibrator 31.
The contour of the resin-molded surface mount type piezoelectric vibrator 31 and the shape of the electrode terminal 33 in the lead frame 60 causes misalignment therebetween due to the above-mentioned difference in coefficient of linear expansion from the center of the surface mount type piezoelectric vibrator 31 and across the width thereof. The misalignment results in a difference in size of the electrode terminal 33 across the width of the surface mount type piezo electric vibrator 31. In the electrode terminal 33 cutting process after the resin molding process, the ends of electrode terminal 33 are cut off from the lead frame 60. The difference in size of the electrode terminal 33 across the width of the surface mount type piezoelectric vibrator 31 can cause contact of a cutting punch with the mold resin thereof, thus resulting in problematic resin chips due to lead cutting. As described above, the resin chipping resulting from resin molding has an adverse influence on the product performance of the surface mount type piezoelectric vibrator 31.
2. The electrical test process for the surface mount type piezoelectric vibrator 31 have required more measurement time because of measurement items for guaranteeing performance characteristics of the surface mount type piezoelectric vibrator 31 and a measurement accuracy in recent years. Much time is therefore spent on the electrical test. Individual surface mount type piezoelectric vibrators 31 are problematically difficult to handle so as to guarantee the performance characteristics thereof.
To ensure the characteristics and reliability of the surface mount type piezoelectric vibrator 31, a resin mold construction is therefore required for the surface mount type piezoelectric vibrator 31. The resin mold construction would allow measurements of the surface mount type piezoelectric vibrator 31 on the lead frame 60 in the electric test and the simultaneous quick batch measurements of more surface mount type piezoelectric vibrators 31. The time reduction would enable resulting saved time to be allocated to measurements for performance characteristic measurement items for measurement accuracy guarantee, thus making it possible to ensure a higher reliability and a higher quality.
3. For the above purpose, a higher cavity density is required for the resin mold construction, which would allow electrical tests performed on the lead frame 60 and allow for the layout of the lead frame 60 for simultaneous batch contact of more electrode terminals. However, the higher cavity density would result in a problematically complicate mold for the resin mold construction.
In other words, contact surface of the mold are inserted between the resultant outer peripheral portion of the above-mentioned resin mold construction to be shaped to enclose the vibrator 6 and the side of the vibrator 6. The outer peripheral portion shaped to enclose the vibrator 6 to support the positional accuracy of a terminal formation portion is to be disposed on the side of the vibrator 6 as a frame 63 for supporting the section bar 62 and the lead terminal. In the mold 66 for forming cavities, therefore contact surfaces between the outer peripheral portion to be shaped to enclose the vibrator 6 and the side of the vibrator 6 and between a section bar 62 and the mold 66 are formed for each cavity. Resin burrs resulting from resin molding include thin burrs produced on the sides of the package and the top surface of the lead frame from a mold clamping clearance between the upper mold and lower mold. To allow the removal of these thin burrs, a mold clamping clearance accuracy is required, as far as thin burrs can be removed, in a position where the contour of the package is to be shaped and in positions of section bars 62. To make a plurality of adjacent cavities closer to one another for a higher cavity density, a sufficient strength is therefore required for narrower section bars 62 and the mold. The mold must also be of a complicated shape that would avoid the shape of section bars 62 together with the maintenance of the accuracy of individual mold clamping clearances.
[Process for Cutting Electrode Terminal Portions]
In a process for cutting electrode terminal portions, each of the dummy terminals 32 and the electrode terminals 33 connecting to the surface mount type piezoelectric vibrators 31 on the lead frame 60 are cut in predetermined positions. This separates individual surface mount type piezoelectric vibrators 31 from the lead frame 60.
In the process for cutting electrode terminal portions of the surface mount type piezoelectric vibrator 31, a notch groove is sometime formed in advance in each cutting point in advance for cutting load reduction. As an adverse influence of this, warpage in the lead frame 60 sometimes results. In other words, the formation of notch grooves in the lead frame 60 can lead to the expansion of notch groove formation surfaces, thus resulting in warpage in these surfaces. Any warpage in the lead frame 60 will make it impossible to proceed with subsequent processes properly when the lead frame is mechanically carried and aligned.
[Electrical Test Process]
An electrical test process for the surface mount type piezoelectric vibrator 31 has required more measurement time in response to measurement items for guaranteeing performance characteristics of the surface mount type piezoelectric vibrator 31 and a measurement accuracy in recent years. Much time is therefore spent on the electrical test.
The electrical test process involves separating individual surface mount type piezoelectric vibrators 31 from the lead frame 60 after resin mold and carrying, positioning and electrically inspecting individual surface mount type piezoelectric vibrator 31 to distinguish between non-defective and defective vibrators. Characteristics of surface mount type piezoelectric vibrators 31 are classified according to users' applications.
Surface mount type piezoelectric vibrators 31 are loaded on tapes and the like according to types such as different load capacity as serial equivalent static capacity and frequency deviation, which completes the surface mount type piezoelectric vibrator 31 manufacturing process.
The longer measurement time is, the more accurate frequency measurements for vibrators 6 will be, whereby the higher the accuracy required is, the longer measuring time will therefore be. It is required to give an assurance whose reliability or quality is improved by assigning reduced time to the measurement time for guaranteeing the measurement items and measurement accuracy of the performance characteristics guarantee so as to secure performance characteristics and reliability of the surface mount type piezoelectric vibrator 31 in case that much time is therefore spent on the test time and the individual translation alignment due to the increase of the measurement time by the measurement items and measurement accuracy for guaranteeing the performance characteristics of the surface mount type piezoelectric vibrator 31.
For the electrical test method described above, a method is known which involves bringing electrical contact terminals into contact with the electrode terminals for simultaneous batch electronic part measurement.
In the electrical test process of the surface mount type piezoelectric vibrator 31, there are the following problems in relation to, in a lump, measuring the surface mount type piezoelectric vibrator 31 by bridging the electrode terminal 33 in electrical continuity particularly with the outer lead 3.
1. A limited number of electronic parts are measured all together in the electrical test method that involves bringing electrical contact terminals into contact with electronic parts mounted in a row on the side frame at a right angle.
2. As shown in FIGS. 38 and 40, on a conventional lead frame 60, piezoelectric vibrators 6 are mounted in two rows at a right angle to the longitudinal direction of two side frames 61 (in the vertical direction in FIG. 40). This requires section bars 62 bridging between the side frames 61 or the frame 63 for supporting lead terminals, and the like. As shown in FIG. 40, there is a limit to the arrangement of piezoelectric vibrators 6 at shorter intervals for a higher density and a limited number of piezoelectric vibrators 6 are measured all together.
3. If, on the other hand, a plurality of surface mount type piezoelectric vibrators 31 are arranged at shorter intervals for a high density and driven to oscillate, the oscillating condition of adjacent surface mount type piezoelectric vibrators 31 and their intervals can affect their oscillation frequency.
FIG. 44 is a diagram showing the oscillation circuit of a common piezoelectric vibrator. CS, represented by a dashed line, refers to stray capacity. FIG. 45 is a graph showing a relation between the load capacity of a common piezoelectric vibrator and frequency deviation. The axis of abscissas CGOUT shows a load capacity while the axis of ordinates shows frequency deviation. It is well known that the oscillation frequency varies with the magnitude of the capacitor CG in FIG. 44, as in the graph shown in FIG. 45. It is also well known that the stray capacity is proportional to the area of wiring connected with the oscillation circuit and inversely proportional to the distance.
It is known from the above fact that the frequency of piezoelectric vibrators 6 also vary between adjacent surface mount type piezoelectric vibrators 31 to be measured in the electrical test process for surface mount type piezoelectric vibrators 31. The distance between adjacent surface mount type piezoelectric vibrators 31 has a different influence on the frequency of the surface mount type piezoelectric vibrator 31. If an attempt is made to meet the necessity of enhancing the layout density of the lead frame relative to the lead frame 60 on which more electrical contact terminals are brought into contact with electronic parts as described above, piezoelectric vibrators 6 can be affected by the influence of the frequencies of piezoelectric vibrators 6 oscillating each other due to the distance between adjacent surface mount type piezoelectric vibrators 31, thus making it difficult to make correct frequency measurements.